Hi Stuart

> will putting a negative cv into a vc-adsr (set manually to a long
> release) achieve this, or will the
> release stage continue at the pace it was set at when the gate was
> released

Nope. As far as I remember the schematics, the parameters can be edited
in realtime - even while the attack/decay/release already has started.

> is there a way to do this with the standard adsr

Not without modifications.

> i suppose a third question would be, how do others implement the
> open/closed hh thing

I do it similar as Kim, but the other way round: the decay is set to the
long time, the release to the short time. This ensures, that a retrigger
stops the open hihat.
The corresponding Audio Example is available at:
http://fa.utfs.org/musik/synthesizer-buch/book-audioexample-31.mp3

Florian